1. Technical Field
The present invention relates to a vibrator element, a sensor device, a sensor, and an electronic apparatus.
2. Related Art
A tuning-fork vibrator element (tuning-fork piezoelectric vibrator element) as an example of a vibrator element is a vibrating member that may be a component element of an oscillator, a sensor device, or the like, and has at least one base part and at least one vibrating arm (vibrating beam) of a piezoelectric material articulated (connected) to the base part.
For example, when a voltage (electric field) is applied to quartz crystal as a piezoelectric material, the quartz crystal is deformed. The quartz crystal develops inductive reactance characteristics like a coil in a particular frequency band near its natural frequency. Electronic component with application of this principle is a quartz oscillator.
A tuning-fork quartz oscillator is manufactured by housing the tuning-fork vibrator element in a package and vacuum-sealing the interior of the package, for example. The quartz oscillator is used as a component part of an oscillation circuit, for example.
Further, the tuning-fork vibrator element may also be used as a sensor device (for example, a force sensing device) for detecting a physical quantity (an acceleration, pressure, an angular velocity, an angular acceleration, or the like). Since the quartz crystal has advantageous temperature stability and a high Q-value, a sensor with high accuracy, high stability, and high reliability is realized using the quartz oscillator. An example of using the tuning-fork vibrator element as a force sensing device is disclosed in Patent Document 1 (JP-A-2006-352771), for example.
FIGS. 30A and 30B are diagrams for explanation of a configuration and a principle of the force sensing device described in Non-Patent Document 1 (W. C. Albert, Force sensing using quartz crystal flexure resonators, 38th Annual Frequency Control Symposium 1984, pp 233-239. As shown FIG. 30A, a tuning-fork vibrator element has a base part MT, two vibrating arms (BE1, BE2) connected to the base part MT, and a weight part AR.
The two vibrating arms (BE1, BE2) vibrate at a resonance frequency in directions perpendicular to an extending direction of the respective vibrating arms. In this state, when an acceleration is applied to the weight part AR, for example, the weight part AR bends in an out-of-plane direction due to an inertia force FC(+) (or an inertia force FC(−) in the opposite direction), and thereby, the vibrating arms (BE1, BE2) are expanded and contracted, and the vibration frequency of the vibrating arms (BE1, BE2) changes as shown in FIG. 30B.
The vibration frequency f of the vibrating arms (BE1, BE2) is nearly proportional to the magnitude of the inertia force FC(+) (or the inertia force FC(−)) applied to the weight part AR and nearly linearly changes. Thereby, by detecting the change of the vibration frequency of the vibrating arms (BE1, BE2), the acceleration may be detected.
Recently, the higher functionality and the reduction in size and weight of an electronic apparatus are advanced, and there are needs for further improvements in detection sensitivity of sensor devices and needs for further reduction in size of the oscillators and sensor devices in response. The development of small vibrator elements that fulfill the needs is an important challenge for the future.
Note that, as a quartz crystal plate, for example, a Z-plate (may be referred to as “nearly Z-plate”) or an X-plate (may be referred to as “nearly X-plate”) is used. The Z-plate (nearly Z-plate) is a quartz crystal plate with a surface (front surface or rear surface) of the crystal plate as a Z-surface (nearly Z-surface) perpendicular (nearly perpendicular) to the optical axis (Z-axis) of the quartz crystal. The Z-surface may be referred to as a surface defined by an electrical axis (X-axis) and a mechanical axis (Y-axis).
Further, the X-plate (nearly X-plate) is a quartz crystal plate with a surface (a front surface or a rear surface) as an X-surface perpendicular (nearly perpendicular) to the electrical axis (X-axis) of the quartz crystal. The X-surface may be referred to as a surface defined by the mechanical axis (Y-axis) and the optical axis (Z-axis).
Downsizing of the tuning-fork vibrator element is described in Patent Document 1, for example.
The tuning-fork vibrator element (piezoelectric vibrator element) described in Patent Document 1 is formed by processing the Z-plate of quartz crystal using photolithography as a semiconductor manufacturing technology.
The direction of the flexural vibration of the vibrating arms is an X-axis direction (a direction along the width of the vibrating arms).
In the technology disclosed in Patent Document 1, downsizing is realized while the resonance frequency of the tuning-fork vibrator element (piezoelectric vibrator element) is maintained by reducing the width of the vibrating arms while shortening the length of the vibrating arms.
Further, suppression of CI-value and suppression of oscillation due to second-order harmonics are realized by forming long grooves along the longitudinal direction of the vibrating arms and employing the vibrating arm shape in which the width dimension of the vibrating arm gradually decreases from the base part toward the leading end, and then, increases.
Patent Document 2 (JP-A-2009-5022) discloses a technology of vibrating arms along the Z-axis direction (the thickness direction of the quartz crystal plate). Note that, in the technology described in Patent Document 2, the quartz crystal plate is only used as an elastic material.
That is, a piezoelectric film is formed on the surfaces of the arm parts made of quartz crystal as the elastic material. As a cross-section structure of the arm parts, a structure in which the piezoelectric film is sandwiched between upper and lower electrodes is employed, and, when a voltage is applied to the upper and lower electrodes, the piezoelectric film flexes along the Z-axis direction.
Further, Patent Document 3 (JP-A-2005-197946) discloses a technology of realizing flat temperature coefficient characteristics by producing vibration B (first-order Z reverse-phase flexural vibration: first-order walk mode) in the Z-axis direction in addition to the vibration A (fundamental harmonic X flexural vibration) in the X-axis direction, coupling the vibration A and the vibration B by nonlinear parametric vibration phenomenon, and compensating for the second-order temperature coefficient of the vibration A.
Furthermore, Patent Document 4 (JP-A-2009-165164) describes a structure in which electrodes are respectively provided on vibrating arm (vibrating rod) front surfaces, rear surfaces, left side surfaces, and right side surfaces in a tuning-fork quartz oscillator (FIGS. 2 and 4 of Patent Document 4 show an example in which grooves are formed in the longitudinal direction of the vibrating arms and electrodes are also formed within the grooves, and further, FIG. 13 describes an electrode arrangement example as a related art).
In addition, Patent Document 5 (JP-A-2008-42794) describes an example of a manufacturing method of manufacturing a tuning-fork quartz oscillator using photolithography.
In order to improve device sensitivity (detection sensitivity) of a sensor device, reduction (downsizing) of the width of the vibrating arms in a vibrator element is effective. However, it is undeniable that, as the width of the vibrating arms is smaller, the distance between the electrodes for applying a voltage (electric field) to the vibrating arms becomes smaller, and short circuit of the electrodes becomes easier to occur. Further, it is also undeniable that the wiring width is forced to be made smaller, and therefore, disconnection of wiring becomes easier to occur.
Furthermore, in the tuning-fork vibrator element having plural vibrating arms, the respective vibrating arms are extended in parallel from the base part toward the first direction. Since the respective vibrating arms vibrate in the width direction of the respective vibrating arms (a second direction perpendicular to the first direction in a plan view, in other words, the arrangement direction of the respective vibrating arms), it is necessary to provide the respective vibrating arms apart at a predetermined distance in the second direction not to inhibit the vibration of one another.
Thereby, reduction in size of the vibrating arms of the tuning-fork vibrator element in the width direction (second direction) (i.e., the reduction of the distances between the respective vibrating arms) have limitations.
Further, in the case where the quartz crystal plate is processed by wet etching, unwanted fin portions (irregular shape portions) are formed on the side surfaces of the respective vibrating arms due to etching anisotropy of the quartz crystal, and the side surfaces of the vibrating arms are not flat in a microscopic sense.
In this case, for setting the distances between the respective vibrating arms, it is necessary to allow for margins (positional margins) in view of the fin portions formed on the side surfaces of the vibrating arms.
In this manner, if the reduction of the width of the vibrating arms is promoted to improve the device sensitivity of the sensor devices, a problem of formation of electrodes and wirings becomes apparent. Further, as downsizing of the vibrator element is promoted, in the tuning-fork quartz vibrator element having plural vibrating arms, also a problem that reduction of the distances between the respective vibrating arms becomes difficult arises.
The quartz vibrator elements (piezoelectric vibrator elements) disclosed in Patent Document 1, Patent Document 4, and Patent Document 5 have a commonality in which the vibrating arm extended in the first direction is flexurally vibrated in the width direction of the vibrating arm. It is undeniable that, if an attempt to further promote the reduction of the width of the vibrating arms and the reduction of the distances between the plural vibrating arms is made, the above described disadvantages become apparent.
Note that Patent Document 2 discloses the vibration of the vibrating arm in the thickness direction of the vibrating arm, however, the vibrating arm in Patent Document 2 does not directly use the piezoelectric effect of the elastic material (quartz crystal plate), but have a special structure for producing flexural vibration by laminating the upper and lower electrodes and the piezoelectric film on the elastic material and using the laminated structure containing the piezoelectric film.
Accordingly, in the case where the quartz crystal plate as the elastic material is also used as a piezoelectric material for producing vibration (that is, a typical quartz vibrator element structure is used), any technology is not disclosed on how the flexural vibration in the thickness direction of the vibrating arm is produced.
Further, Patent Document 3 discloses a technology of flattening the temperature characteristics of the sensor device by secondarily producing the flexural vibration in the thickness direction of the vibrating arm. Note that the vibration in the thickness direction in this case is absolutely the secondary vibration, the fundamental vibration is the traditional flexural vibration in the width direction of the vibrating arm, and the secondary flexural vibration in the thickness direction is only added to the fundamental flexural vibration.
Furthermore, in the technology disclosed in Patent Document 3, there is no study or suggestion on promotion of downsizing in view of improvements in device sensitivity of the sensor device using the vibrator element or promotion of downsizing of the vibrating arm in the width direction of the sensor device.